The function of a variable spring support is to support loads (forces) on PDE through the PDE's range of displacement that potentially can damage PDE while in operation. These forces include loads introduced to the PDE by pressure, temperature, vibration, wind, earthquake, dynamic transients and/or the PDE's own weight effects. The variable spring support should minimize one or more of the following typical problems related to industrial/commercial PDE:                1) Piping stress in excess of that permitted in ASME piping codes.        2) Leakage at pipe joints, ductwork joints or equipment connections.        3) Excessive forces and moments on connected equipment such as pumps and turbines.        4) Excessive stresses on adjacent supporting and restraining elements (e.g. adjustable supports or non-adjustable).        5) Resonance with imposed or fluid-induced vibrations.        6) Interferences due to thermal expansion and contraction with adjacent PDE.        7) Disengagement of piping from its supports.        8) Minimize the need for expansion loops in piping systems.        
Mechanical and ASME piping codes and other international standard codes establish general rules for evaluating flexibility in piping systems. Spring supports are commonly utilized to increase flexibility on piping systems to satisfy allowable loads on equipment nozzles. It is imperative that loads be limited to meet applicable codes. The need to satisfy thermal and gravitational loads on sensitive equipment in a piping system is just as viable for movements measured in thousands of an inch as it is for large movements of several inches.
In contrast, hard supports (meaning supports without a spring), adjustable or non-adjustable, cannot provide flexibility to piping systems, correct piping misalignment or rectify problems with fabrication tolerances. Particular to rotating equipment, the result of using a non-adjustable support is often evident in seal damage, casing distortion and coupling misalignment. Static supports can result in over stressed conditions, which lead to expensive equipment failure, down time and even injuries. The cost of down time is usually more expensive than the equipment itself. Without the use of a spring, extra flexibility must be incorporated into a piping system by means of expansion loops to limit thermal displacements and substantially reduce excessive forces on equipment nozzles. Adjustable (type) supports such as a rod hanger or adjustable base elbow or base line support can cause more damage to equipment if they are not properly adjusted.
A spring support is cheap insurance against down time and expensive repairs. More importantly, spring supports extend PDE life. A spring support on load sensitive equipment and load sensitive fluid carrying media (i.e. glass lined piping) provides assurance that the proper support load is applied. This is particularly true during and after the initial stages of an industrial/commercial plant's operating cycle when external loads due to vibration and unbalanced loads tend to exceed the normal operating range.
Although coil spring supports have been proven in industry to solve critical stress problems in PDE, the application of coil spring supports can be improved. Coil springs do not directly address small movements effectively. Design engineers are reluctant to use a coil spring support where thermal pipe expansion and/or equipment displacements are small (e.g. 1/16″). Space limitations are often controlling factors near sensitive equipment. The helical wound coil spring support is too large an apparatus to typically install under piping or equipment in some instances. This limitation is also magnified by piping and HVAC insulation requirements that must be recognized as well.
Carbon steel coil springs are also vulnerable to corrosive agents in the air and from accidental liquid spills. On occasion, acid or caustic and corrosive materials spill from vessels, pumps and other equipment creating conditions where corrosive materials attack the spring support, thus, shorting its life. In the same way, air born particles such as salt air can attack the carbon steel material of the spring support. For corrosive services, protective coatings such as neoprene can be applied to the carbon steel coil spring. Manufacturers recommend neoprene only for operating temperatures up to 225 degrees Fahrenheit. It is also common practice to paint and galvanize carbon steel spring supports in used in corrosive environments as well. This may provide some protection but the spring itself cannot be inspected through routine maintenance while the spring is in service. No guarantee can be assured that the inner working parts are corrosion free while it is assembled.